(1) Summary of the Invention
The present invention relates to an improved reusable syringe which on the plunging stroke of a piston injects a liquid through a needle into an animal and which refills with the liquid upon retraction of the piston from a supply means and referred to herein as a "back-fill syringe". In particular, the present invention relates to a reusable syringe which is filled at an end opposite the needle from a disposable syringe mounted in a handle of the reusable syringe used to inject the liquid from the reusable syringe.
(2) Prior Art
In the prior art, the supply means for the syringe is a bottle or other container with an opening to the outside which allows air to move into the container as the fluid is dispensed. This prevents a vacuum inside the container. U.S. Pat. No. 2,374,368 to Mejia discloses a valved reusable syringe with an open supply reservoir. U.S. Pat. Nos. 1,995,971 to Dowling and 3,353,537 to Knox et al describe two valve reusable syringes. U.S. Pat. No. 4,204,539 to Brugge discloses a hand operated reusable syringe with two valves. Other reusable syringes or injection devices are disclosed in U.S. Pat. Nos. 2,645,224 to Beebe; 2,757,670 to Ogle; 2,821,193 to Ziherl; 2,821,195 to McLintock; 3,400,716 to Schultz; 3,738,539 to Beich; 4,261,359 to Chein and 4,530,695 to Phillips.
Another syringe apparatus is described in Russian Pat. No. 933,101 to Timoshin. This patent describes a single-hand operated veterinary instrument for injecting livestock which incorporates systems for automatic sterilization of the injection needle and for disinfection and marking of the injected area with a colored disinfectant solution. A syringe, injection needle holder and ejector, and a bellows operated pump are mounted on a pistol-type grip body. The inlet of the syringe is connected by plastic tubing and a two-way valve to a bottle of veterinary preparation. The outlet is connected by plastic tubing and a sleeve to the injection needle. The inlet of the bellows is connected by plastic tubing to a bottle of colored disinfectant solution. The outlet is connected by plastic tubing and a sleeve to a spray on the injection needle holder. The ejector comprises a spring loaded striker which is activated by a trigger lever, the length of travel being controlled by stops. This device is complicated and has external hoses across the pistol grip body of the syringe which can easily become detached or damaged.
None of these prior art patents describe a reusable syringe which is mated to a disposable syringe so that the use of a tube connected to reservoir or a bottle mounted on the syringe can be avoided. There is a need for a compact, inexpensive, simple hand held device.